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CHOOSING THE RIGHT SYNTHETIC FIBREThere are a large variety of synthetic fibre options available in the market. These include micro and macro synthetic

fibres, glass fibres, cellulose fibres, kevlar fibres, carbon fibres, blended fibres and other specialist fibres. With so

many options it can be difficult to determine exactly what fibre is required for a given application. One of the major

issues facing the fibre reinforcement industry today is not only the lack of knowledge from the customer, but the

incorrect use of fibres by the fibre supplier and concrete supplier. For this reason it is especially important that any

supplier can verify their product with extensive testing and project references. Follow the simple steps below to

ensure your fibre choice is the best one for you.

STEP ONE – ENSURE CORRECT FIBRE TYPE

The first step to choosing the right fibre is to understand the type of fibre required for your application. Globally, the

two main standards for fibre reinforced concrete are British Standard EN14489 and ASTM C 116-03

International Standard ASTM C 116 -03, Standard Specification for Fibre Reinforced Concrete and Shotcrete,

outlines 3 general classes of fibre reinforced concrete;

Type 1 – Steel fibre reinforced concrete or shotcrete Type 2 – Glass fibre reinforced concrete or shotcrete Type 3 – Synthetic fibre reinforced concrete or shotcrete

British Standard BS EN 14489, Fibres for concrete, Part 2: Polymer fibres – Definition, specifications and conformity,

covers fibre manufactured from;

“polymeric material such as polyolefin, e.g. Polypropylene or polyethylene, polyester, nylon, pva, polyacrylic, aramids

and blends of them.”

It divides polymer fibres into two main classes according to their physical form, as follows:

Class I: Micro Fibres

Class Ia: Micro Fibres < 0.3mm in diameter, mono-filamented Class Ib: Micro Fibres < 0.3mm in diameter, fibrillated

Class II: Macro Fibres > 0.3mm in diameter.

Class I micro fibres should be used for plastic shrinkage control, impact protection, anti - spalling and fire control.

Class I Micro Fibres are not a structural reinforcing fibre and cannot be used to replace welded wire mesh or any

structural steel elements.Class II structural macro fibres

can be used as a replacement for crack control mesh or as structural reinforcementin concrete or shotcrete. BS EN14889 states that; “Class II fibres are generally used where an increase in residual

(post-cracking) flexural strength is required

STEP TWO – ENSURE FIBRE PERFORMANCE

Slab on Grade Performance

When specifying with fibres you should not think in terms of volume per cubic metre, but in overall post crack

toughness, also known as post crack flexural capacity.

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For concrete, the standard industry performance indicator for fibre is the Re3 value. Re3 is measured with standard

beam tests in a third point loading arrangement. The Re3 is the average load applied as the beam deflects to 3mm,

and is expressed as a percentage ratio of the load of the first crack.

The UK Concrete Society states that “fibre dosage should be sufficient to give an Re,3 value of 0.3, otherwise the

concrete should be treated as plain.”

Many applications will require an Re3 value of higher than 30%. Warehouse floors often require an Re3 performance

closer to 50%. In this instance the onus is on the fibre supplier to present beam testing from certified testing facilities

that clearly demonstrate the performance criteria can be met. While an excellent indicator, it is always prudent to

conduct additional testing to ensure the performance of the fibre in the specific concrete mix.

The UK Concrete Society’s Technical Report No. 34; Concrete industrial ground floors, A guide to design and

construction can be used to determine the Re3 value for your project. (Request a copy from EPC).

Shotcrete Performance

Shotcrete performance is measured via post crack energy absorption testing (also called toughness) expressed in

Joules. Toughness is tested using the ASTM C1550 Round Determinate Panel Test or The EURONORM EN-14448

EFNARC Panel Test.

Fibre suppliers should be able to supply documentation from NATA approved testing facilities that their fibre can meet

the required joule specification using one of these tests.